1. Field of the Invention
This invention relates to hydration control of cementitious systems and more particularly to the use of neutralized salts of .alpha.-monohydroxy di- and multifunctional carboxylic acids to obtain hydration control.
2. Description of the Related Art
Hydration control refers to control over the setting time of cement, i.e. controlled retardation followed by subsequent activation of cement hydration. Hydration control is useful in a number of different situations, e.g. in the reclaiming of unused concrete such as described in U.S. Pat. No. 4,964,917, in situations where concrete is prepared at a remote location and subsequently transported to the worksite in a set delayed state for reasons of expense and/or convenience such as described in U.S. Pat. No. 4,676,832 for cementing operations carried out, e.g. in offshore platform grouting, and in shotcrete applications where long worktimes followed by very rapid set are often required.
Hydration control may be desired from initial mixing or at some later time after hydration has already begun. In the situation where the cementitious composition is prepared at a remote location and then transported to the worksite, retardation is desired from the outset with subsequent activation at some later point. In other situations, e.g. the reclaiming of concrete, hydration of the cement has already begun but needs to be retarded for a period of time, generally overnight or for a weekend, until it is desired to use the concrete.
Hydration control has been achieved in some situations using two different admixtures, i.e. a retarder to delay the set and an accelerator to activate the set of the cementitious system. However, many of the materials commonly employed as retarders are acidic, e.g. gluconic acid, citric acid and phosphoric acid, having a pH of less than 2.5, while most of the traditional accelerators are basic, e.g. strongly alkaline solutions of silicates and aluminates, having a pH greater than 12 and therefore, both admixtures are undesirable from environmental and safety standpoints.